The 25-year-old has been with the Roar on a short-term deal since September after being brought in to cover the injured Massimo Murdocca.

Karlovic was born in Adelaide, played for Adelaide City Force before heading to Italy to further his career.

United coach Aurelio Vidmar indicated he was interested in signing the midfielder in his post-match media conference.

"We've spoken to his agent but that's all we've done at this point at time," he said.

Roar coach Ange Postecoglou said the club wished Karlovic all the best for the future.

"He did a great job for us. He came to the club at a time where unfortunately all the turmoil was happening, change of coaches and the club going on a bad run," Postecoglou said.

"To his credit he worked hard and was very professional and I think he did a good job for us.

"But we are at a point now where for me I've got a group of players I want to work with until the end of the year and make some decisions on. With injured players coming back we'll be right to cover it."

Karlovic's signature would be a bonus for the Reds who have already signed Nigel Boogaard in preparation for the upcoming Asian Champions League.

Vidmar said the Mariners player would add further depth to his squad.

"I think that's a fantastic signing. He was really keen to come here and we are really happy to have him, I think he's got a fair bit of experience for such a young defender and he's going to add a lot of value to our team," he added.